Pattern measuring apparatus

ABSTRACT

An object of the present invention is to provide a pattern measuring apparatus which performs high-accuracy concavity/convexity determination (e.g., distinguishing between a line segment and space) while simultaneously reducing the dose of a beam falling onto a pattern to be measured. To attain the object, this invention proposes a pattern measuring apparatus which specifies a pattern in a measurement object area by scanning a tilted bean with respect to another area different from the measurement object area and then performs measurement based on the pattern-specifying result. With such arrangement, it becomes possible to perform measurement without the risk of wrong pattern designation while lowering the dose of a beam hitting the measurement object area.

BACKGROUND OF THE INVENTION

The present invention relates generally to pattern measuring apparatuswhich perform pattern measurement based on pattern concavity/convexitydetermination or the like, and more particularly to a pattern measuringapparatus that performs pattern identification of line segments and gapspaces formed on a semiconductor wafer.

A scanning electron microscope (SEM) is one form of charged particlebeam apparatus, which enables observation of fine objects. The SEM has avariety of applications, including measurement and inspection of circuitpatterns that make up highly integrated semiconductor devices.Incidentally, with recent advances in miniaturization of semiconductordevices, circuit patterns increase in integration density. Inparticular, this has often led to appearance of ultrafine circuitpatterns, known as line-and-space patterns having successive linepatterns, wherein lines and gap spaces are hardly distinguishable fromeach other in interval or pitch. Additionally, with advances insemiconductor microfabrication technology, observation images of a lineand space are becoming more similar in look to each other.

An increase in visual similarity of line and space results in the riskthat one of them is mistaken for the other. More specifically, even whenan image was acquired in order to measure the width of a line, it canhappen in practice that the width of a space is measured by mistake.Japanese Patent Literature JP-A-2004-251674 (its corresponding UnitedStates Patent Application Publication is US 2004-A-0222375) disclosestherein a technique for distinguishing between line and space portionson the basis of expansion of hem parts of a plurality of peaks containedin a differential waveform of a profile, which has been obtained byapplying projection processing to an image acquired. However, sensedimages tend to decrease in contrast due to further miniaturization inrecent years; so, it is difficult in some cases to extract thedifference in brightness of hem parts of profile peaks. Once peaksoverlap each other, discrimination can be failed.

JP-A-2006-332069 (its corresponding United States Patent is U.S. Pat.No. 6,872,943) discloses a technique for performing concavity/convexitydetermination with high accuracy by irradiating a tilted beam andemphasizing a difference between peaks of two, right and left edges of aline.

SUMMARY OF THE INVENTION

The techniques as disclosed in the above-cited Patent Literatures are toenable distinction of lines and spaces that have traditionally beendifficult to be distinguished over each other. Especially, the techniquetaught by JP-A-2006-332069 is capable of emphasizing a differencebetween the right and left edges of a line, thus making it possible toenhance the success rate of concavity/convexity determination. However,as the beam is irradiated obliquely with respect to the pattern beingmeasured, an image to be obtained by such beam irradiation is an obliqueimage, which is unsuitable for use in accurate measurement of patternsizes. Although it is also permissible to perform size measurement byscanning a beam for the measurement use (beam with no tilt) after havingcompleted the concavity/convexity determination, a need is felt to applyto the pattern under measurement both the beam scanning forconcavity/convexity determination and the beam scanning for sizemeasurement.

By taking into consideration the adhesion of electrification charge dueto beam irradiation and pattern shrink, it is desirable that the beamirradiation onto the measurement object pattern stay less. Proposedbelow is a pattern measuring apparatus capable of performinghigh-accuracy concavity/convexity determination (e.g., line/spacedistinction) while at the same time suppressing the irradiation amountof a beam falling onto a pattern under measurement.

To attain the foregoing object, in accordance with one aspect of thisinvention, a pattern measuring apparatus is provided which specifies apattern in an object area under measurement by scanning a tilted beamwith respect to an area different from the measurement object area andexecutes measurement based on the specified result.

With the arrangement stated above, it becomes possible to performmeasurement without the risk of wrong pattern designation whilesimultaneously lowering the dose of a beam hitting the measurement area.

Other objects, features, and advantages of the present invention willbecome apparent from the following description of embodiments of thepresent invention provided in relation to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing one example of a scanning electronmicroscope (SEM).

FIG. 2 is a diagram showing a profile change in the case of a protrusionis image-sensed from the direction of ±θ.

FIG. 3 is a diagram showing a positional relationship between an area ofan image used for length measurement and an oblique image area in thecase of the oblique image being acquired while performing image pickupof the length measurement-use image.

FIG. 4 is a diagram showing an example in which an oblique image and alength measurement-use image are contained in one display screen image.

FIG. 5 is a flow chart showing a measurement process including aconcavity/convexity determination step.

FIG. 6 is a diagram showing a cross-sectional view of a patternfabricated through a self-alignment double patterning (SADP) step.

FIGS. 7A to 7C are diagrams each showing a profile of a sensed image ofthe SADP-formed pattern.

FIG. 8 is a diagram showing a beam locus upon irradiation of a tiltedbeam.

FIG. 9 is a diagram showing a beam locus when a field of view is movedfrom the ideal light axis.

FIG. 10 is a diagram showing an example having a concavity/convexitydetermination area and a length measurement area within a line-and-spacepattern formation area.

FIG. 11 is a flowchart showing a process for executing pattern lengthmeasurement through the concavity/convexity determination ofline-and-space pattern.

FIG. 12 is a diagram showing a positional relation of an addressingpattern, concavity/convexity decision area and measurement object area.

FIG. 13 is a diagram for explanation of an example which measures adeviance between an image of the concavity/convexity decision area andits design data.

FIG. 14 is a flowchart showing a process of determining a pattern formedby SADP.

FIG. 15A is a graph showing a relation of focus value versus focusposition; and,

FIG. 15B is a diagram showing one example of a focus position correctiontable.

DESCRIPTION OF THE EMBODIMENTS

An explanation will now be given below of an apparatus for measuringpattern sizes by using either image data obtained by an image sensingdevice or waveform data, examples of which apparatus include a patternmeasuring apparatus that executes desired measurement by accuratelyspecifying a target pattern to be measured.

A scanning electron microscope (SEM) which irradiates an electron beamonto a semiconductor circuit pattern and detects secondary electrons tobe derived therefrom to thereby evaluate the shape of a circuit patternthat is the object of interest will be described below as an example ofthe image sensor device, although other charged particle beam devices,such as a focused ion beam (FIB) device or like equipment, mayalternatively be employed as the imager device.

Embodiment 1

In the embodiment below, an example will be described which tilts anelectron beam within an area different from the measurement object(i.e., area unused for length measurement) in the process of acquiring alength measurement image that is subjected to pattern measurement anduses the information to be obtained based on irradiation of such tiltedbeam to perform concavity/convexity determination. By the beam tilting,the electron beam is caused to hit one side-wall of a circuit patternrather than its top surface; so, this sidewall increases in width ofwhite band when compared to top-down images. As the white band varies inwidth in a way depending on a tilt angle of the electron beam, itbecomes easier to specify an edge on one side with the white bandgetting thick. A sidewall onto which the electron beam is irradiated isa sidewall of convex portion. Thus, if this edge is specifiable, itbecomes possible to specify the positions of convex and concave portionswith respect to this edge.

More concretely, in the case of tilting the beam by using the swing-backaction of an objective lens, it is understood that when the sidewall isused as a reference, a convex part (line) is positioned in the beamswing-back direction for beam tilt whereas a concave part (space) isplaced in the reverse direction to the swingback direction. In thisembodiment, the concavity/convexity determination is achieved byevaluation of the electron beam's tilt angle and the extensity of thewhite band at that time. Additionally, in areas used for circuit patternlength measurement, it is possible to perform length measurement withhigh accuracy because image pickup is done in the state that the tiltangle is returned to vertical beam angle.

In accordance with the embodiment explained below, the line-and-spaceconcavity/convexity determination is carried out by irradiating a tiltedelectron beam with respect to an area which is not used for lengthmeasurement whereby it becomes possible to achieve high-accuracyline-and-space concavity/convexity determination in a short period oftime, which is substantially the same as an image pickup time consumedto simply sense a length measurement image.

In addition, it is no longer necessary to perform a plurality ofscanning operations with the tilt angle varied. Thus, the irradiationamount or “dose” of the electron beam is lowered. This makes itexpectable to reduce chargeup and shrink of a sample, also known asworkpiece. The intended image is acquirable by a single scan. It is thusunnecessary to execute positioning between an oblique image and lengthmeasurement image. This makes it possible to perform theconcavity/convexity determination in a simple and easy manner.

Practical embodiments will be described in detail with reference to theaccompanying drawings below.

(Overview of Scanning Electron Microscope)

An explanation will first be given of a scanning electron microscope(SEM) in accordance with one embodiment of the invention. As shown inFIG. 1, the SEM of this embodiment is generally made up of varioussystem components including, for example, an electron source 101 whichirradiates a primary electron beam 108 onto a workpiece wafer 106, anacceleration electrode 102, a focusing lens 103, a deflector 104, anobjective lens 105, a detector which performs sampling of an emissionelectron signal 109 to be generated from the sample wafer 106 to therebyacquire a digital image, a digitizer 111, an image memory 116 whichstores therein the acquired digital image and performs displaying orprocessing, an input/output (I/O) unit 118, an image generation unit115, an image processing unit 114, a system control unit 113, a resultstorage unit 120, and a database (DB) module 117 for storage of recipedata, called the recipe unit 117. It should be noted that in theexplanation below, a main operational constituent that performsconcavity/convexity determination and length measurement or the likewill also be called the arithmetical unit.

The electron source 101 is the one that emits a primary electron beam108. The acceleration electrode 102 is for accelerating primaryelectrons. The focusing lens 103 is to perform focusing of the primaryelectron beam. The deflector 104 performs two-dimensional (2D) scanningdeflection of primary electrons. The objective lens 105 focuses primaryelectrons onto the sample wafer 106. A stage 107 is for stably mountingthe sample thereon. The detector 110 detects an emission electron signal109 of secondary electrons generated from the sample. The digitizer 111digitizes a detected signal. A deflection control unit 112 controls adeflection amount or the like in the deflector. Respective ones of thesecomponents are connected to the system control unit 113 via a bus 119.

The pattern measuring apparatus have other components, including theimage memory 116 for storage of image data, the image generator 115 thatperforms image creation processing, the image processing unit 114 thatperforms processing of an image acquired, the recipe unit 117 thatstores a recipe(s) containing therein inspection conditions, data entrydevices for giving instructions to the device, such as a keyboard and apointing device called the mouse, the I/O unit 118 made up of a displaymonitor and/or a printer for outputting data from the device, and theresult storage unit 120 for storing measurement and inspection results.These components are interconnected together by the bus 119.

This embodiment device also functions to form a profile based ondetected secondary electrons or reflection electrons or else. Thisprofile is formed by execution of projection processing based on anelectron detection quantity at the time of performing one-dimensional(1D) or two-dimensional (2D) scanning of primary electrons or based onbrightness information of an acquired image. The profile obtained is foruse in size measurement of patterns fabricated on a semiconductor wafer,for example.

The SEM of this embodiment further includes a beam tilting deflector 805shown in FIG. 8, which is provided for irradiating an electron beamwhile obliquely inclining or tilting the beam with respect to its ideallight axis 802 (i.e., the loci of a beam that is not deflected). Thebeam tilting deflector 805 serves to deflect an electron beam 801 at anobject point 803 of the objective lens 806 to thereby change the angleof an arrival point at which the electron beam 801 falls onto sample807. The electron beam 801 that was deflected by the beam tiltingdeflector 805 to the right side of a drawing sheet is defected againtoward the ideal light axis 802 by the swing-back action of objectivelens 806. By letting the object point 803 be a deflection support point,it becomes possible to irradiate the electron beam 801 at anintersection point of the sample 807's surface and the ideal light axis802.

(SEM Image Acquisition)

Next, SEM image acquisition in the embodiment device will be explainedwith reference to FIG. 1. Acquisition of an image is such that severalconditions are set up in conformity with the recipe that was taken outof the recipe unit 117; then, digital image data is acquired. Theprocessing for image acquisition is as follows.

Firstly, the electron source 101 emits primary electron beam 108, whichis accelerated by the acceleration electrode 102. Subsequently, rays ofthis beam are gathered together by the focusing lens 103, deflected bythe deflector 104, and thereafter focused again by the objective lens105 to fall onto the sample wafer 106 at a target location on the topsurface thereof. By the irradiation of this primary electron beam 108,an emission electron signal 109 is generated from the sample surface,the intensity of which signal is detected by the detector 110 and isthen converted by the digitizer 111 into a digital image signal.

The signal as output from the digitizer 111 is sent to the imagegenerator unit 115, which performs processing including pixelmultiplication, digital filtering and others, thereby providingprocessed digital image data which is stored in the image memory 116.

Then, at the image processor unit 114, frame addition-average processingis applied to the digital image data as read out of the image memory 116in a manner that one input line is processed at a time.

Additionally, by irradiating the electron beam while simultaneouslytilting it by the beam tilting deflector 805 shown in FIG. 8, it ispossible to acquire an oblique image of the sample. In this embodimentdevice, an area that is not used for length measurement is acquired in aslanted manner at the time of sensing a length measurement image. Thisoblique area is used for the line-and-space concavity/convexitydetermination.

FIG. 2 shows a profile change in the case of a convex portion beingimage-sensed from a direction of +θ or −θ. Here, a half-value width ofprojection in the direction of +θ is represented by HP1, HP2; ahalf-value width of projection in the direction of −θ is given as HM1,HM2. In the case of image pickup being performed from the −θ direction,the half-value width HM1 of a signal of an edge portion on the left sidebecomes greater; in the case of image pickup being done from +θdirection, the half-value width HP2 of a signal of an edge on the rightside becomes larger. Although in this embodiment the half-value width ofa peak is used as the reference, this is not to be construed as limitingthe invention. Any position of the peak may be used therefor as far asit increases or decreases in length depending on the tilting of theelectron beam.

As the half-value width of an edge signal in the image pickup directionbecomes larger in this way, use of this phenomenon makes it possible toachieve the line-and-space concavity/convexity determination based on anincrease or decrease of the half-value width.

More specifically, when the width of a profile that was obtained bytilting the electron beam with respect to its light axis increases inthe electron beam scanning direction, it is decidable that a portionwith formation of a sidewall (edge) in the electron beam tiltingdirection exists at a location corresponding to the profile. In otherwords, when the measured extensity of a detection signal in the linearscan direction (i.e., X direction in the case of 2D scanning) becomeslarger than that in the case of irradiating the electron beam along itslight axis, it is determinable that an edge surface exists on theelectron beam tilt direction side. Conversely, when the width of theprofile becomes smaller, it is determinable that the object of interestis a portion corresponding to a rear surface (opposite side) whenviewing from the tilt direction of the electron beam. That is to say, itcan be seen that in cases where one of two peaks appearing in the eventof obliquely scanning the electron beam becomes larger in width whereasthe other becomes smaller, either a concave or convex portion existstherebetween. Additionally in this state, when a peak with itsincreasing width exists on the electron beam tilt side, it is decidablethat a concave portion is present; when a peak with its decreasing widthexists on the electron beam tilt side, a convex portion exists.

A further feature of this embodiment is that image pickup is performedwhile moving the tilt direction relative to an image region which is notused for length measurement of the sample as shown in FIG. 3 to therebyacquire an oblique image and a length measurement image simultaneously,the oblique image being for use in the line-and-spaceconcavity/convexity determination stated supra.

In accordance with this embodiment, there is no need to performrepeatedly the scanning for concavity/convexity determination and thescanning for length measurement. This suppresses the irradiation amountor “dose” of such electron beam. Thus it is possible to reduce damage tothe sample.

FIG. 5 is a flow diagram of one exemplary automated measurement process.First, SEM conditions are set up (at step 501). Examples of the SEMconditions as used herein include optical conditions, such as anelectron beam acceleration voltage, beam current and so forth, andmeasurement object portion (coordinate) information. Then, a lengthmeasurement range and tilting condition are set (at step 502). In caseswhere one frame is designed to contain a mixture of the lengthmeasurement object area and concavity/convexity determination area (thisis not the length measurement object area), both ranges are set in sucha way as to ensure achievement of a signal amount needed for the lengthmeasurement and establishment of a signal amount enabling successfulexecution of the concavity/convexity determination. Next, beam scanningis carried out within a range including the measurement object portionbeing set up (step 503). For the concavity/convexity determination area,tilt scanning is performed (step 504). For the region that is set as thelength measurement object area, normal scanning without tilting isperformed to form a top-down image (step 505).

After having completed the scanning stated above, the arithmetical unitexecutes concavity/convexity determination based on the informationextracted from a tilted-beam irradiation area and the above-statedjudgment criterion (at step 506, 507). Checking whether or not theconcavity/convexity determination is succeeded is as follows: a whiteband (peak) value of a sidewall opposing the beam coming from the beamtilt direction (swing-back direction by means of the objective lens),for example, is compared with a predetermined value; when the former isgreater than or equal to the latter, a decision of success is made. Thisdecision of successful completion of the concavity/convexitydetermination may alternatively be made in the case of a peak valuedifference from a sidewall on the opposite side is larger than or equalto a prespecified value. Still alternatively, in case the beam is tiltedin different directions, one of which is for an upper side region of thelength measurement object area and the other of which is for a lowerside region thereof as shown in FIG. 3, the decision that theconcavity/convexity determination was succeeded may be made when it isverified that both of them are in success. Additionally, in the case ofa pattern being formed obliquely, the peak width of one edge increasesfrom time to time without regard to the tilt direction as an example; ifthis is the case, the concavity/convexity determination may be performedby also taking into account the increased width size or “fatness” ofsuch edge of the length measurement object area. In this case, thesystem may be arranged to perform either concavity/convexitydetermination or pattern inclination determination by reference to theedge data of length measurement object area when a difference in widthbetween the right and left edges of length measurement object area isgreater than or equal to a predetermined value.

In case it is decided that the concavity/convexity determination wascompleted successfully, a length measurement value is calculated basedon a preset measurement condition (at step 508). For example, if themeasurement condition is to measure the width of a line pattern, thenmeasure the size of a distance between edges of this pattern. In thiscase, a length measurement box is set at both edges of the pattern to bemeasured; then, measure a peak-to-peak distance of brightness profilewithin the box.

In the case of the concavity/convexity determination being judged to bein fail, an error message is issued to prompt a system operator(s) tomake a decision as to what kind of action should be taken thereafter(step 509).

A result of superposition of a concavity/convexity determination profileand acquired image is shown in FIG. 4. As shown herein, an image isacquired by switching between the tilted scanning and non-tiltedscanning within one frame whereby the information required for theconcavity/convexity determination and the information needed formeasurement are to be included in a single image (i.e., image signalincluded in one frame). Thus, it becomes possible to reduce the risk ofdesignating a wrong measurement object. It is also possible in a postverification event to check whether the correct measurement object isselected by just seeing a single display screen.

The switching between the tilted beam irradiation state and normal beamirradiation state based on the beam deflection at a locking position isexecutable by turn-on/off control of the beam tiltingdeflector-theoretically, no appreciable irradiation position is moved.Thus, it is possible to minimize the risk of pattern selection mistake.

Owing to the ability to achieve the concavity/convexity determinationusing one frame information, there is no need to perform multiplescanning operations. It is thus possible to prevent throughputdegradation while at the same time suppressing pattern shrink due toexcessive beam irradiation. This makes it expectable to improve thereproducibility of length measurement.

Embodiment 2

An explanation will next be given of an example which performsconcavity/convexity determination of a workpiece or sample wafer by atechnique other than the beam tilt method, which utilizes the swing-backaction of an objective lens. FIG. 9 is a diagram showing part of anoptics system of SEM including a couple of scrolling deflectors 901 and902.

Although these scrolling deflectors 901-902 are for deflecting a beamwhile letting an intersection of a principal plane of objective lens 806and an ideal light axis 802 be a supporting point of deflection, anotherarrangement may be employed which supplies the deflector with a signalwith superimposition of a 2D beam scanning signal to thereby perform theview field movement and the deflection for beam scanning. Alternatively,the scanning deflector 104 and the scrolling deflectors 901-902 may beprovided separately.

FIG. 10 is a diagram showing an example with setup of a lengthmeasurement object area 1002 and concavity/convexity determination area1003 in a line pattern fabrication region 1001. Positioning is performedby means of the sample stage in such a manner that the light axis of anelectron beam coincides with the coordinates of a central point of thelength measurement object area 1002, then causing a visual field to movefrom such state by a distance Δx. In the case of such view movement,also known as scrolling, deflection is performed with the intersectionof the objective lens's principal plane and ideal light axis being asthe deflection support point as in the example shown in FIG. 9. Thus,the beam behaves to obliquely fall onto the sample at an angle formedwith the sample surface as shown in FIG. 9. In this embodiment theconcavity/convexity determination is executed by utilizing this tiltedstate.

In the example of FIG. 10, the concavity/convexity decision area 1003includes three line patterns 1007 as shown in a magnified image 1005.Among these three line patterns, there are space portions 1009, e.g.,trench-like grooves. Due to the tilted beam irradiation, the image is inthe state that sidewalls 1008 of the line patterns are visible. Thisimage is used to prepare a brightness profile 1006, resulting insidewall edges (sidewalls 1008) in the opposite direction to the viewmovement direction being seen to be thick. Thus, it becomes possible toperform the concavity/convexity determination of a pattern(s) includedin the concavity/convexity decision area 1003 based on the brightnessprofile prepared. Furthermore, the positional precision of such viewmovement by electromagnetic deflection or electrostatic deflection isvery high; so, it is possible to perform deflection of Δx accurately.Consequently, when the concavity/convexity determination is executablein the concavity/convexity decision area 1003, it is possible to specifya convexo-concave surface configuration 1010 of patterns included in thelength measurement object area 1002 that lies beyond the area 1003 by apredetermined distance.

Since the sizes of line width and gap space width are predefined bydesign data, it is also possible by the concavity/convexitydetermination to readily specify a pattern at a position which is movedby a predetermined distance from the pattern that was identified by theconcavity/convexity determination.

FIG. 11 is a flowchart showing a process of performing measurement basedon the concavity/convexity determination. First, a wafer is introducedinto a vacuum sample chamber (at step 1101). Then, the sample stage isdriven to move the wafer so that its surface area to be measured isplaced at a position immediately beneath the light axis of an electronbeam (step 1102). FIG. 12 is a diagram showing the positionalrelationship between a measurement object area 1201 andconcavity/convexity determination area 1205. In step 1102, the samplestage is moved so that the measurement area 1201 locates at a positionbelow the electron beam's light axis. Next, an image of addressing area1202 is acquired (step 1103), followed by execution of addressing (step1104). In this addressing, the position of an addressing pattern 1204 isspecified by template matching techniques using a pre-registeredtemplate. The addressing pattern 1204 lies outside of a line-and-spacepattern fabrication area 1203. A specific pattern that is unique inshape has been selected therefor.

As the addressing pattern 1204 and the measurement object area 1201 arein a known positional relationship, it is possible by specifying theposition of addressing pattern 1204 to accurately perform the viewmovement toward the measurement area 1201. In this embodiment, prior tomoving the view to the measurement area, the view is shifted to theconcavity/convexity decision area 1205, thereby executingconcavity/convexity determination (at step 1106). Since the positionalrelation between the measurement area 1201 and concavity/convexitydecision area 1205 is also known, the view movement of from theaddressing pattern 1204 to concavity/convexity decision area 1205 isalso executable based on the known information. In a case where theconcavity/convexity determination is judged to be succeeded, the view isshifted to the measurement area 1201 (step 1107); then, execute lengthmeasurement (step 1108). If the concavity/convexity determination isfailed, any one of the following corrective actions is taken (at step1109): measurement is performed again; measurement is skipped; and, anerror message is issued to prompt the system operator to take remedialaction for avoiding occurrence of measurement interruption accidents.

With the above-stated arrangement, it becomes possible to perform theintended measurement based on accurate pattern identification by meansof the concavity/convexity determination, without having to performexcessive bean irradiation onto the measurement object area 1201. Thusit is possible to reduce the risk of beam irradiation damages withrespect to the object being measured, thereby suppressing the influence,such as sample shrink or the like. This leads to achievement of atechnical advantage as to improvement in length measurementreproducibility.

Although the accuracy of the view movement by the deflector is highenough to enable execution of precise concavity/convexity determinationas far as the positional relationship of patterns is approximate to thatdefined in the design data, undesired determination with half-pitchdeviation can still be made, resulting in a line pattern being misjudgedto be a gap space. In this respect, an example capable of attaining moreaccurate specifiability will be explained, which specifies a deviationof view field on a display screen for the concavity/convexitydetermination use and correct such deviation accurately to therebysituate the view in the measurement area.

This example is arranged so that the arithmetical unit evaluates adeviance between an image of concavity/convexity determination area andits corresponding design data and shifts the view field by a distanceequivalent to such deviance during positioning of the view in themeasurement area. FIG. 13 is a diagram showing a case where aconcavity/convexity decision area image 1301 is deviated from itsinherent view position. Comparing it to design data 1302 of pre-acquiredconcavity/convexity decision area reveals that the view is positioned ata location deviated by a distance Δx₁. In this state, when the view ismoved by a predefined distance value toward the measurement area, itwill possibly happen that the view of the length measurement area isdeviated undesirably. This deviance is corrected for compensation bysupplying the scroll deflector with a deflection signal for correctingthe distance Δx₁. More precisely, processing is performed to obtain theposition of a center of mass or “centroid” for a respective one ofdesign data and real images. The resultant centroid positions aresuperposed together, thereby obtaining a deviance therebetween, fromwhich is computed a deflection signal for correction of this deviance.This deviance compensation signal is then supplied to the deflector.

By performing deviance correction using an on-screen display image ofthe concavity/convexity decision area in the way stated above, itbecomes possible to accurately locate a view field for the lengthmeasurement use at the exact position. The view position correction maybe replaced with a process of adjusting the position of a lengthmeasurement box by a distance corresponding to the deviance statedsupra.

Although in this embodiment the concavity/convexity determination isperformed based on the information gained from the concavity/convexitydecision area 1003, this may be modified in various ways, one example ofwhich is as follows: another concavity/convexity decision area 1004 isprovided to permit the decision of success in concavity/convexitydetermination to be made when it is verified that the both areas areconsonant with each other in concavity/convexity determination results.Additionally, the concavity/convexity determination and the imageacquisition of concavity/convexity decision area may be arranged so thatthese are performed after having acquired an image of length measurementobject area and yet before execution of the length measurement.

Although the above-stated arrangement is the one that concernsconcavity/convexity determination of patterns, autofocusing may also beimplemented simultaneously during scanning of a concavity/convexitydecision area (at step 1105).

However, in the case of Δx₁ being large in value, a deviance Δf 1503takes place between a focus position 1501 of concavity/convexitydecision area and a focus position 1502 of length measurement objectarea as shown in FIG. 15A.

In this case, in light of the fact that Δx₁ is a known value, a properlyfocused image is acquirable by preparing in advance a focus positioncorrection table 1504 shown in FIG. 15B, which defines therein the focusposition with Δx₁ and the deviance Δf of focus of the length measurementobject area, and then performing correction or “amendment” of the resultof autofocusing performed in the concavity/convexity decision area.

By using the above-stated method, it is no longer necessary to performthe scanning for the autofocusing separately, thus making it possible toobtain an advantage as to improvement of throughput in addition to theimprovement in accuracy of concavity/convexity determination.

Embodiment 3

The above-stated pattern distinguishing method using a tilted beam isemployable not only for convexo-concave patterns, such as line-and-spacepatterns, but also for the specifying of circuit patterns that arefabricated by self-alignment double patterning (SADP) techniques.

FIG. 6 shows a cross-sectional view of a pattern in SADP process step. Acircuit pattern formed by the SADP process has multiple line segments,two adjacent ones of which make one set together in compliance withmanufacturing process rules. This means that linear circuit patternsegments having the same cross-sectional shape appear alternately. Forthis reason, in order to measure pattern sizes properly, it is requiredto identify the period λ of circuit pattern accurately. In FIGS. 7A to7C, projection waveforms in Y-direction are shown, which are obtainedwhen SADP-fabricated pattern is image-sensed while changing the tiltangle of an electron beam from zero to −θ and to +θ. By changing thebeam tilt angle by ±θ, the image's visual appearance varies depending onthe pattern's rounded shape at its top portion. Looking at the pattern'speriod, the following relation is given: 2×λ1=λ2=λ3.

Accordingly, it is possible by performing pattern measurement based onthe oblique image acquisition and position detection, which have beendiscussed in the embodiments stated supra, to accurately perform theintended size measurement of one set of circuit patterns chosen as thelength measurement object, without mistaking the measurement position.

FIG. 14 is a flowchart of the processing for determining the period inSADP process. The above-stated embodiment method is used to acquire anoblique image and an obliquity-free image for use as the lengthmeasurement object (referred to hereinafter as the length measurementimage) in steps 1401 to 1404. Then, at step 1405, projection processingis applied to each image, thereby obtaining the brightness profilesshown in FIGS. 7A-7C.

While in the embodiments 1-2 the concavity/convexity determination isperformed using the half-value width of brightness profile, the SADPprocess is such that period judgment is performed using a peak value(s)of brightness profile and a position(s) thereof because of the fact thatthe visual brightness (luminance value) varies as shown in FIG. 6.

The oblique image's peak position is obtained with the lengthmeasurement image's peak value being as a reference. In case the obliqueimage and length measurement image are different in pixel number fromeach other, their native values are not directly usable for comparison.Therefore, this comparison is done after having applied normalization tothe brightness profiles, followed by execution of peak positiondetection (step 1406).

The peak position detection may be performed by various methods otherthan the above-stated method, including self-correlation using a singleoblique image and intercorrelation of two oblique images.

The SADP-formed pattern shown in FIG. 6 has gaps, including core gaps(i.e., gaps defined between upstanding sidewalls) and spacer gaps (gapsdefined between slanted sidewalls). These two types of gaps aredifferent in fabrication process from each other; so, measurement withwrong designation leads to the lack of an ability to perform properprocess evaluation. For example, a peak which is observed brightly bythe oblique image with tilt angle −θ is at the left edge of a core gapwhereas a relatively darkly seen peak is at the right edge of core gap.Thus, it becomes possible to perform proper measurement of a targetobject, by specifying the type of a gap or the kind of pitch from aprestored relationship of tilt direction versus peak brightness.

In light of the fact that the interval of peak positions detected ineach brightness profile is expected to have the periods λ1, λ2 and λ3 asshown in FIGS. 7A-7C, in case the relation given by 2×λ1=λ2=λ3 does notwork out, it is decided that the period judgment is failed. If this isthe case, any one of the following actions is taken (at step 1409):measurement is performed again; measurement is skipped; an error messageis displayed, thereby prompting the system operator to take correctiveaction to avoid measurement interruption.

Finally, a peak position of length measurement image that is the closestto the peak position of oblique image detected in step 1406 becomes atthe measurement position of the length measurement object (at step1407), followed by execution of length measurement (step 1408).

With the arrangement stated above, it is possible to perform measurementbased on accurate pattern identification relying upon the cycle judgmentwhich has been difficult by mere use of a length measurement image,without having to excessive beam irradiation onto the measurement objectarea.

It is needless to say that in this embodiment also, effects andadvantages of the aforesaid embodiments are expectable.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A pattern measuring apparatus, comprising: an arithmetical unit fordetermining a pattern size by using a signal to be obtained based onscanning of a charged particle beam emitted from a charged particlesource; and a beam tilting deflector for irradiating the chargedparticle beam while tilting this beam with respect to an ideal lightaxis thereof, and wherein the arithmetical unit specifies a kind of apattern formed on a sample based on a signal to be obtained by obliquelyscanning the beam in an area of the sample being different from an areaused to obtain the pattern size.
 2. The pattern measuring apparatusaccording to claim 1, wherein the beam tilting deflector specifies thekind of a pattern formed on the sample based on a signal obtained whenirradiating the tilted beam in an area in which is formed the same kindof pattern as that of the area used to obtain the pattern size.
 3. Thepattern measuring apparatus according to claim 1, wherein the beamtilting deflector deflects the charged particle beam in such a mannerthat the charged particle beam goes away from the light axis of anobjective lens.
 4. The pattern measuring apparatus according to claim 3,wherein the beam tilting deflector switches between a tilted state and anon-tilted state of the charged particle beam during scanning of a oneframe by means of a scanning deflector which is for scanning the chargedparticle beam.
 5. The pattern measuring apparatus according to claim 1,wherein the beam tilting deflector is a deflector for moving a visualfield.
 6. The pattern measuring apparatus according to claim 5, whereinthe arithmetical unit specifies the kind of the pattern based on asignal obtained in an area with the visual field having been moved by apredetermined distance from the area in which the pattern size isobtained by the deflector for moving the visual field.
 7. The patternmeasuring apparatus according to claim 1, wherein the arithmetical unitdetermines whether the pattern formed on the sample is a line pattern ora space.
 8. The pattern measuring apparatus according to claim 1,wherein the arithmetical unit determines whether the pattern formed onthe sample is a core gap or a spacer gap.
 9. A pattern measuringapparatus having an arithmetical unit for determining a pattern size byusing a signal to be obtained based on scanning of a charged particlebeam emitted from a charged particle source, wherein the apparatuscomprises a beam tilting deflector for irradiating the charged particlebeam while tilting this beam with respect to an ideal light axis thereofand wherein the arithmetical unit specifies a kind of a pattern formedon a sample based on a signal to be obtained by obliquely scanning thebeam in an area of the sample being different from an area used toobtain the pattern size, thereby to measure the pattern thus specified.10. The pattern measuring apparatus according to claim 9, wherein thearithmetical unit determines that the pattern formed on the sample iswhich one of a line, a space, a core gap and a spacer gap.